Art of heating air for gas turbine use



Sept. 9, 1969 M. K. DREWRY 3,465,517

ART OF HEATING AIR FOR GAS TURBINE USE Filed Dec. 26. 1967 2 Sheets-Sheet 1 it //Z 30 .23 1

| j I I 5 II I x I I l I I I l INVENTOR Z/ MONTROSE K. DREWRY ATTORNEYS P 9, 1969 M. K. DREWRY 3,465,517

ART OF HEATING AIR FOR GAS TURBINE USE Filed Dec. 26, 1967 2. Sheets-Sheet 2,

FLAME BOUNDARY INVENTOR MONTROSE K. DREWRY 15a ATTORNEYS United States Patent "ice US. Cl. 60-39.06 14 Claims ABSTRACT OF THE DISCLOSURE A method of heating air using a gas turbine combustor having an air tube for receiving a flow of compressed air, a conical casing having its downstream end sealed within the tube and having an apex at its other end with an opening of a size that accommodates a nozzle of a type to discharge a hollow conical spray pattern within the conical casing, the external angle of the spray pattern being greater than the internal angle of the casing and being so directed as to leave a conical clearance space between the conical casing and spray pattern substantially throughout the length of said conical casing, with said clearance space of progressively decreasing size outwardly, and said conical casing having uniformly and closely spaced holes beginning about one-third of the way outwardly from the nozzle, the arrangement being such that spontaneous ignition continues under adverse circumstances and that uniform air-oil ratios occur throughout and the relatively slow burning hydrocarbons become hydrolyzed to highly combustible alcohols, a1- dehydes, carbon monoxide and hydrogen.

BACKGROUND OF THE INVENTION Field of the invention The gas turbine combustor and combustion method of the present invention is directly applicable to gas turbines presently employed in a wide variety of applications such as in aircraft, in electric generators, and in land and sea transportation, wherever moderate size power units are needed.

Description of the prior art In my co-pending patent application No. 533,214, now Patent No. 3,360,929 a gas turbine combustor is disclosed in which there is a guiding cone supported within a conical apertured casing to form a mixing space between the guiding cone and casing for receiving a hollow conical spray of oil. In this prior disclosure the spray pattern wipes the conical casing beginning about half way out. This arrangement, including the guiding cone, does not give a short, clean, flame, and there is elemental carbon which takes a relatively long time to burn. While the arrangement of my prior application is satisfactory for many uses, it is not suitable for uses where space and weight are critical, where the cost of metal is important, where a clean, blue flame is required, and where flameout must be positively prevented.

Conventional oil-fired combustors generally employ two stages, the first stage burning the oil with about its theoretical requirement of air so that ignition may be sustained, and the second one mixing the products of combustion with the four to six times of additional air in order to lower the temperature to a level that the gas turbine can use reliably. Schiefer Patent No. 2,974,485 calls these two stages Primary and Secondary, and

3,465 ,5 l 7 Patented Sept. 9, 1969 it stresses the need of using the proper amount of air in the primary mixing and combustion zone. General practice has indicated that heretofore two stages are positively necessary to avoid serious loss of ignition (flame-out) when oil flow or air How ,are varied appreciably and independently during typical and emergency operation. Continuity of adequately heated air to the turbine is obviously vital, and therefore by far most combustors presently employ two stages. Some references describe a third stage relating to cooling the air or metal, and in some few combustors the oil is vaporized in heating surfaces within the combustor before firing, thus substituting for the first stage. In conventional combustors the two stages are not totally adequate. Because of limited dynamics of chemical, thermal and kinetic nature, flames persist throughout the air-cooled flame tube, and carbon enters the gas turbine.

The value of short, clean flames, where the prior art has been so deficient, is more than simply reducing the size of the combustor substantially. Incomplete combustion of the carbon causes erosion of the turbine blades, usually its most serious source of trouble. If erosion becomes excessive carbon can clog the combustor or coat the turbine blades, thus reducing power output and increasing the fuel required. In some applications the smoke which results from conventional combustors is objectionable. Also, carbon increases the radiation to metal parts and thus increases their temperature substantially more than the radiation which results from nonluminous flames such as those produced from alcohols, aldehydes and product gases. Uniformity of temperature is obviously important in limiting temperature differences in the combustor and turbine parts and in minimizing the possibility of premature failures. A design that affords uniform outlet temperature, such as that afforded by the present invention, actually permits higher average turbine temperatures with substantial fuel economies. With the present invention combustion occurs at a relatively low uniform temperature which is substantially the same as the temperature of the gases which are about to enter the turbine. Erosion from ash in the fuel and air can be limited in some cases because the l5002000 F. combustion temperature does not fuse the ash and make it more abrasive as in usual combustors.

SUMMARY OF THE INVENTION Combustion improvement in gas turbine combustors is the general object of the present invention, and this is provided by a construction and method wherein most of the relatively slow burning hydrocarbons of fuel oil are converted by hydroxylation to alcohol and other highlycombustible and clean-burning gases that are still more combustible than hydrogen, one of the most explosive gases. An incidental object of the invention is to simplify the construction of combustors and to shorten the length theref. The latter is accomplished by an arrangement wherein there is a more rapid combustion and greater uniformity of temperature in the improved combustion process. The improved process and apparatus minimizes the possibility of flame-out even under extremely adverse conditions, thereby rendering the combustor highly reliable. With the present invention the efliciency of the combustor is substantially improved while reducing size, weight and cost, the normally slow-burning oil vapors being converted to highly combustible blue flame gases so that flame-out is prevented, the flames being so short and clean that combustor cost is reduced and turbine performance is improved.

A further object of the invention is to provide an improved combustor so designed that a single stage is adequate, because the function of spontaneous ignition and thermal dilution are combined through use of a novel method and arrangement.

Hydroxylation of slow-burning hydrocarbons to fastburning alcohols, aldehydes, carbon monoxide and hydrogen, which hydroxylation is an important feature of this invention, is facilitated principally because of favorable environment for chemical reaction of the oil vapor and air at limited temperature and turbulence. Practically simultaneous mixing of all the air with all the oil, in uniform proportions and in a very small space, results in hydroxylation and combustion at a limited temperature, usually of some 1500 to 2000 F. for present gas turbines, as contrasted with the first stage temperature of the present conventional combustor which reaches local peaks of probably 2500 to 3000 F., since the no-heat-loss temperature with the usual stoichiometric air quantity and 500 F. air inlet is 400 F. The former 1500 to 2000 F. temperature range favors oxidation of the hydrocarbons to alcohols, aldehydes, carbon monoxide and hydrogen, whereas with the latter higher temperature, in the many localities of deficient oxygen, hydrocarbons are cracked to elemental carbon that requires a greatly increased period of time to burn than do combustible gases. This truth is evidenced by the usual relatively very short blue flames resulting from combustion of alcohols, aldehydes, carbon monoxide, and hydrogen.

With the above and other objects in view the invention consists of the improved gas turbine combustor and method of combustion and all of the parts, combinations and steps as set forth in the claims, and all equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing, in which the same reference numerals designate the same parts in all of the views:

FIG. 1 is a partially diagrammatic longitudinal sectional view through a gas turbine for aircraft use, showing how the combustor of the present invention is employed;

FIG. 2 is a similar partially diagrammatic view showing how the combustor of the present invention is employed in connection with a turbine for driving an electric generator;

FIG. 3 is a longitudinal section view through a portion of a combustor tube illustrating the improved invention;

FIG. 4 is a fragmentary enlarged view through the conical casing portion showing the processes which occur in the hydroxylation-combustion zone and adjacent two typical air orifices in the casing;

FIG. 5 is a longitudinal sectional view through the nozzle;

FIG. 6 is an enlarged fragmentary sectional view of a portion of a conical casing showing an alternative type of air opening;

FIG. 7 is a view similar to FIG. 6 showing another type of air opening; and

FIG. 8 is a fragmentary view of a portion of a conical casing showing an alternative arrangement of air holes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more particularly to the drawing, first to FIG. 3, the numeral 10 designates an air tube through which air from the compressor which conventionally serves a gas turbine is flowing in the direction indicated by the arrows. This air may be propelled by the compressor 11 of FIG. 1 or 111 of FIG. 2. Mounted within the air tube 10 (FIG. 3) is a conical casing 12 having an apex with an opening 13 for receiving a nozzle 14. The nozzle 14 is better illustrated in FIG. 5. It is a well known type which delivers an oil spray S in the form of a hollow cone. A typical nozzle of this type is manufactured by the Lucas Gas .4 Turbine Equipment, Ltd., Birmingham, England. Oil is delivered into the nozzle under suitable pressure by way of a pipe 16 which communicates with the annular space 17 of FIG. 5. The oil from the annular space 17 is introduced into the swirl chamber 19 tangentially through ports 20 and 21. This causes the oil to leave the nozzle outlet 22 at high rotation and thus with a high centrifugal force which produces the hollow cone type of fine spray pattern. The valve 23 in an oil return duct 24 may be adjusted to sustain the rotation of the oil and obtain a desired fineness, form and size of the spray pattern. The oil return may direct the surplus oil back to the oil tank. Referring to FIG. 3, the radial width W of the spray opposite the outer air holes 25 should be between 10-50% of dimension D (FIG. 3) and preferably about one-sixth of D, which dimension is the length along the slant height of the conical casing 12 measured from its apex to the outer end of the grouping of air holes 25.

The tube portion 10 contains the air to be heated which is usually at a temperature in the neighborhood of 500 F. as it comes from the compressor 11. The tube portion 10' accommodates the heated air and the flue gases which are moving toward the turbine 7 of FIG. 1. The temperature of the gases G in the tube portion 10 is usually in the neighborhood of 1500-2000 F. in present gas turbines.

The conical casing 12 which separates the tube portions 10 and 10 is apertured beginning approximately onethird of the way outwardly from the nozzle. These apertures 25 are arranged in closely-spaced formation. Each hole is small, and its diameter is between 1%-4% of the distance D in FIG. 3. The portion of the length of the casing designated by H constitutes the major hydroxylation and combustion zone. The portion designated by D constitutes a minor hydroxylation and combustion zone.

In the preferred embodiment of the invention the holes are outwardly flared as at 26, FIG. 4. In certain installations it may be less expensive to have straight drilled holes such as the holes 25a of FIG. 6. It is also possible to have frusto-conical holes such as the holes 25b of FIG. 7, with the largest diameter portions of the holes facing inwardly. The holes are closely spaced and concentrated in order that the mixing of air and oil and the hydroxylation and combustion may be at or near the uniform outlet temperature of 1500-2000 F. for the gases in the tube portion 10. There is a sharp decrease in the velocity of the fine spray drops by the time they reach the hydroxylation-combustion zone which is adjacent the apertured portion of the conical casing. Before the oil spray drops leave the major zone H of the conical casing they are either totally evaporated or have been caused to assume the direction of flow of the air jets which are near the outlet end of the conical casing 12.

The distance D, FIG. 3, between the oil nozzle and the first circumferential row of air holes 25, constituting the minor hydroxylation and combustion zone, is an important factor in obtaining optimum performance. This distance will vary somewhat, depending in part upon combustor size, ambient pressure, oil pressure, nozzle oil flow, and atomization fineness. The distance D is preferably approximately one-third of D but may be in the range of 15%-50% of D so that H is between 50%-85% of the length of the spray pattern. This distance D also, incidentally: affects the amount of initial hydroxylation.

The reliable and eifective aspirating force of the oil jet from the nozzle 14 is employed to induce highly combustible hydrolyzed hydrocarbons, air, and flames from the hydroxylation-combustion zone H in FIG. 3 to the oil nozzle to cause continuous ignition of the oil at its source. Due to the fact that there are no apertures in the conical casing at portion D except small apertures 35 hereinafter referred to, there are no high velocity air nor gas currents to extinguish the flames in this region. Continuity of ignition and combustion will, therefore, be' reliable throughout an unusually wide range of air-fuel ratios and even under adverse conditions. The many small jets that penetrate the outer two-thirds of the spray pattern afford a large area for the major hydroxylation reaction to occur wtih the evaporated oil, after which combustion follows, both processes occurring at a temperature which is substantially the same as the temperature of the flue gases which are about to enter the gas turbine.

Referring now to FIG. 4, this illustrates the processes which are occurring near two typical air openings 25 which are closest to the nozzle. Air flow is represented by the letter A, this flow is in the form of a jet which travels transversely across the oil spray with the jet of gradually decreasing cross-section to the point A. Rapidly evaporating oil drops OD are flowing toward the right and are being progressively evaporated so that the number of oil droplets in each subsequent air jet A is less. The air jets decrease in cross-section because the oxygen reacts with the oil vapors first by hydroxylation, as indicated at H, and then by combustion as indicated by C. Air mixes with the products of combustion throughout its flow beyond the apexes A of the air jets, the mixture of air and products of combustion being designated PCF in FIG. 4, and this mixture being in the presence of flames which result from hydroxylation and combustion. Hydroxylation requires one-third to one-half of the stoichiometric air for combustion. Hydroxylation begins at temperatures as low as 400 F. PCHF adjacent the arrows indicates the products of hydroxylation and combustion which are accompanied by flames which are flowing toward the oil nozzle.

The relatively small air holes 25 encourage hydroxylation because they create a large area of weatherlike fronts around the peripheries of the air jets A where the oil vapor and air chemically interact, these fronts being mixing zones. The air jets causing the hydroxylation taper almost to a point, as at A, as they penetrate through the oil spray pattern S. The oil-air front is not itself visible because all of the space between the air jets is filled with blue flames.

In FIG. 4, flow caused by aspiration of the oil spray due to the entrainment of boundry gases into spaces between its drops is represented by arrows pointing toward the nozzle and traveling both externally of the spray pattern and within it. Externally of the spray pattern the hydrolyzed oil vapor and flame HF is induced toward the nozzle. Internally of the spray pattern S the products of combustion and hydrolyzed oil vapor and the flames (PCHF) likewise flow toward the spray nozzle 14, the products of combustion obviously containing oxygen. In both of these lines of flow HF and PCHF the velocity is low, with limited turbulence, and thus with limited hydroxylation and combustion.

Upon entering the spray as at E, the above two sets of gases mix and burn, evaporating some of the oil spray and hydrolyzing some of the resulting vapors. This action aids in sustaining combustion and particularly during adverse conditions, such as the adverse conditions that may be occassionally encountered by aircraft when suddenly encountering a deluge of rain. In such a case if the displacement of air by steam does not drop the air-oil ratio below one and one-half times stoichiometric air, hydroxylation and thus high combustibility will continue. Assuming normal air is four to five times the chemical requirement, steam can displace two and one-half to three and one-half (four to five minus one and one-half) multiples of air without losing high combustibility. High altitude ignition, diflicult because of low compressor pressures and temperatures, is aided substantially because of the considerably higher combustibility of hydrolyzed hydrocarbons, as in the present invention, than with the relatively slow-burning hydrocarbons of usual combustors.

In stationary gas turbines the sudden total loss of electrical generator load might cause destructive over-speed unless the oil feed rate is instantly reduced drastically.

Since the ignition must be retained for immediate return of the load, this high excess air flow must not extinguish the flames. The present invention solves this problem, principally because of the high combustibility of the gases it causes and insures at the spray apex.

The air holes 25 of FIG. 3 which have flared entrance ends 26 have a discharge coefficient of .95 and, therefore, pass 50% more air than would be passed by the holes 26a of FIG. 6 which have a discharge coeflicient of only .63. In addition, the holes of FIG. 3 assist performance generally and lessen combustor cost. In some cases the simple drilled hole of 25a of FIG. 6 may suflice. For very small gas turbines such as those used in automotive duty today, where dust may tend to clog, the small chamfered ports 25b like those of FIG. 7, may be practical.

While the closely-spaced grouping of holes throughout the apertured area, as shown in FIG. 3, is preferred, there are some cases where a variance in this arrangement may be desirable. For example, it may be desirable at only the beginning of the apertured area H to have a pattern such as shown in FIG. 8 where there are unapertured areas which are V-shaped in plan view to reduce the flow resistance for oil drops and vapor at the beginning of zone H. It may, in certain cases, also be desirable to otherwise vary the hole arrangement, especially at the entrance end.

For initial ignition there is an ignition tube 27, FIG. 3, which is served by flame from an outside source. This is controlled by a valve 28. Tube 27 is employed in the start-up until the combustor is operating normally. Thereafter the valve 28 is closed, as no air should enter through the tube 27 when the combustor is in normal operation.

Inasmuch as the ignition tube 27 is close to the source of oil and remote from the high velocity air inlets 25, a minimum heat input through the pipe 27 will cause ignition.

The optimum included angle of the conical casing 12 depends upon several variables of which oil spray fineness is predominant. The fineness of the oil spray pattern S increases with the angle of the pattern. It is important to note that the external angle of the oil spray pattern S is such that there is a clearance space X between the spray pattern and the interior of the conical casing 12, which clearance space extends substantially throuhgout the length of the conical casing, as shown in FIG. 3. The clearance at X near the casing should be 4-6% of the distance D and preferably 5%.

The penetration distance of the air jets A into the stream of combustion products varies with the diameter of the holes 25. Depending upon the thickness of the oil spray pattern, the air hole diameters may be varied longitudinally to obtain proper penetration.

The distance D of the first circumferential row R of air holes from the oil spray apex should be within the range previously stated and preferably about one-third of the length D of the sloping side of the conical casing in order to perform the function of preventing flame-out under emergency conditions and also to obtain the best hydrxylation and combustion. The oil nozzle spray pattern should be adjusted to produce a pattern such as shown in FIG. 3 to provide the proper clearance space X between the outside of the spray pattern and the inner surface of the conical casing 12. In other words, the angle of the spray pattern of the nozzle should be adjusted so that its external angle is greater than the included angle of the conical casing 12, substantially as shown in FIG. 3. The nozzle spray pattern can be varied by changing the amount of oil rotation and thus the amount of centrifugal force within the nozzle and also by changing the diameter of the exit hole 22 (FIG. 5). By having the clearance space X substantially the length of the conical casing there is adequate flow area for the aspirated oil vapor and flame outside of the spray pattern S. The included angle of the spray pattern is also such that there is adequate space for backward flow internally of the spray, such as the flow designated PCHF in FIG. 4. Lessening of the internal angle of the spray pattern may be used where it is desired to reduce oxygen flow to the nozzle when carbon tends to form locally due to high temperature.

The concentration of the air holes 25 in a compact group beginning about one-third of the way outwardly of the nozzle results in carbon-free combustion. In the usual combustor where there is a single row of air holes or where there are isolated air holes in the zone of the first stage, locally high temperatures occur with resultant cracking to carbon.

With applicants arrangement, where there are contiguous rows, a single level of temperature is insured, thus avoiding carbon and resulting in a uniform outlet temperature. The concentration of the air holes also has the advantage of minimizing the combustor size. In addition, the flaring of the entrance ends as at 26 increases the flow approximately 50% and further decreases the combustor size. The flares 26 also serve to concentrate the hydroxylation and combustion zone for better performance. The total hole area should be 30% 60% of the area of the portion of the casing covered by the holes, and it cannot exceed approximatel 60% of said area without unduly weakening the casing. Thus there is appreciable space between the jets A for oil vapor passage.

The clearance X, FIG. 3, should be suflicient to take care of adverse conditions when much air is present, with little oil, or vice versa. When emergency conditions require oil flow reduced to about with full-load air flow, flame-out must not occur, because flame is to be needed promptly when there is a return to the normal output.

FIG. 1 represents in partially diagrammatic form the use of the improved combustors of the present invention in connection with a gas turbine of the type used in aircraft. In this figure air enters the compressor 11 from the left, as indicated by the arrows, and the compressor 11 propels the air at increased pressure through ducts 30 leading to the combustors 12. In aircraft there are usually four to eight ducts 30, each with a combustor. There may, however, be any desired number. The air heated in the combustors, in the manner heretofore described, leaves the conical casings 12 at substantially the same temperature as the temperature of combustion and is delivered to the turbine 7 to drive the latter, the turbine blade 7 driving the compressor fan 11 through the shaft 31, as is conventional. The aircraft propelling power results from the large volumes of hot gases, represented by the arrows 32, which jet at high velocity from the turbine discharge to cause thrust in the direction of flight.

FIG. 2 illustrates diagrammatically the use of the improved invention in gas turbines for generating electricity. Here the shaft 131 is extended to drive the electric generator 133, the hot gases being discharged as at 132 at relatively low velocity.

The present invention brings about an improved method of heating gases for turbine use. This method includes the steps of spraying oil from the source such as from the nozzle 14 in a finely-divided condition in the form of the hollow diverging conical spray pattern S, directing a multiplicity of air jets, by means of the holes 25, into the spray pattern throughout its length and periphery in the zone indicated by H in FIG. 3, which zone preferably begins approximately one-third of the distance outwardly from the nozzle, as indicated by the designation D of FIG. 3. In this method the zone H constitutes a major hydroxylation and combustion zone. The improved method includes the use of the conical casing to shield the spray pattern S from all other air except that admitted through the holes 25, while maintaining locally uniform oil-air weight ratios to cause combustion to occur in the zone H at relatively low temperatures, which are substantially uniform throughout the zone H, said temperatures being substantially equal to the temperature of outlet discharge as indicated by the arrows G in FIG. 3. The method also includes the causing of flames, highly combustible hydroxylized hydro-carbons, and products of combustion containing air to be continually aspirated from the major zone H to the minor zone D' as indicated by the arrows PCHF and by the arrows HF in FIG. 4, said aspiration bringing about commencement of hydroxylation and combustion in the minor zone, acting to sustain combustion and prevent flame-out even under abnormal conditions, and acting to eliminate carbon formation.

From the above it is apparent that with the improved invention, wherein the outlet temperature at G is substantially the same as the combustion temperature in the major combustion zone H, this tends to minimize temperature differences in the combustor and turbine parts, and thus minimizes the possibility of premature failures. Where the outlet temperature of the gases at G is uniform, higher temperatures in the turbine are permitted, with resultant fuel economies.

The use of many small air jets 25 instead of the small number of relatively large air jets, as is conventional, brings about efficient mixing with a minimum of energy. For the same length of jet A, the total jet area exposed for mixing is inversely proportional to the jet diameter. The small jets A in the present combustor have the additional advantage of causing mixture of practically all of the oil with practically all of the air almost instantaneously, thus avoiding temperature peaks and bringing about clean and rapid combustion.

The velocity of the air jets must be adequate to penetrate across the radial width W of the spray pattern. Jets from the holes 25 which are farthest downstream are naturally deflected toward the outlet by the heated prodnets of combustion from jets closer to the nozzle, and intermediate jets will be deflected proportionately less, but each will have the opportunity to react with its share of fuel. By supplying air in excess of the theoretical requirement adequate oxygen for hydroxylation and combustion in every case is assured. The penetration distance of the air jets A into the stream of combustion products varies with their diameter. Depending upon the thickness of the air spray pattern the air hole diameters may be varied to obtain proper penetration.

The very high rate of hydroxylation and combustion in the relatively small space tends strongly to unify outlet temperatures. Here turbulence is present, and the amount of separation between holes is slight. This is an important leveling influence.

Calculations based upon tests and theory indicate that the combustion rates with the present invention in typical service will approach closely to the theoretical maximum of million B.t.u./hr./cu. ft. The highest rate for conventional combustors is understood to be 60 million B.t.u./ hr./ cu. ft. so that the present combustor is approximately one-third of the size of conventional combustors.

Reference to FIG. 3 will show that the spray pattern S has such an external angle that oil cannot contact the easing 12 because it is separated by the clearance space X which provides adequate flow area for the aspirated oil vapor and flame. The included spray angle is such that there is likewise adequate area for the backward flow PCHF of FIG. 4. This aspirating force is so effective and reliable that introduction of air at the nozzle is ordinarily unnecessary. In some few cases, admission of small amounts of air supplementary to aspirated gases in the near vicinity of the nozzle may be desirable, such as the air holes 35 of FIG. 3, in order to attain total hydroxylation.

The approximately one-third the usual size of the present combustor may permit the use of fewer combustors in certain uses at considerable economies. When gas turbines are developed to cope with temperatures perhaps as high as 2500 F., theory indicates that the high reaction rate of hydroxylation will continue to prevail in this particular design, thus tending to assure the considerable benefit of this invention into the future, as the hydroxylation and combustion temperature in the major zone of the present combustor can be between 15002500 F.

In the claims where reference letters D, D, X, X and W are employed, such letters refer to zones or distances illustrated in FIG. 3, and designated by such reference letters.

What I claim is:

1. The improved method of burning liquid fuel in air to produce hot gases, suitable for driving a gas turbine or the like, that comprises spraying liquid fuel in a diverging jet of hollow conical shape, and projecting a multiplicity of small individual jets of combustion air transversely into the outer surface of said conical spray of fuel to penetrate it inwardly at closely spaced intervals in a band disposed outwardly from the apex of said conical spray jet and shielding the fuel spray from external combustion air in a band located between said first band and the apex of the fuel spray cone to permit reverse flow of the air-fuel mixture toward the apex of said fuel spray cone in a manner to effect uniform ratios of air and fuel conducive to hydroxylation of the liquid fuel that transforms the fuel into highly combustible gases for burning at uniform low temperature without forming elemental carbon.

2. In a method of heating air for turbine use where there has been initial ignition, the steps of spraying oil from a source of finely divided condition and in the form of a hollow diverging conical spray pattern, directing a multiplicity of air jets inwardly into the spray pattern in a major hydroxylation and combustion zone beginning a substantial distance outwardly from the spray source and continuing throughout the remainder of the length of the spray pattern while maintaining a minor hydroxylation and combustion zone between said spray source and the beginning of said major zone, shielding the spray pattern around said minor hydroxylation and combustion zone and maintaining locally uniform oil-air weight ratios in said major hydroxylation and combustion zone to cause hydroxylation and combustion to occur at relatively low temperatures which are substantially uniform throughout said major zone, with said temperatures substantially equal to the outlet temperature of discharge gases from said major zone, maintaining aspiration spaces externally of and within said spray pattern, permitting reverse flow of the air-fuel mixture toward the apex of the oil spray cone, and causing flames, highly combustible hydroxylized hydrocarbons, and products of combustion containing air to be continually aspirated through said aspiration spaces from said major zone back to said minor zone to bring about commencement of hydroxylation and combustion in said minor zone, to prevent flame-out, and to prevent carbon formation.

3. A method as claimed in claim 2 in which the major hydroxylation and combustion zone extends for approximately the final two-thirds of the length of the spray pattern.

4. A method as claimed in claim 2 in which the major hydroxylation and combustion zone extends 50-85% of the length of the spray pattern.

5. A method as claimed in claim 2 in which the hydroxylation and combustion temperature in the major zone is between 1500 and 2500 F.

6. In a gas turbine combustor having a tube for receiving a flow of compressed air and having a nozzle within said tube with its axis extending longitudinally of the tube and being of a type to discharge oil in a finely divided spray pattern which is of hollow diverging conical form, a conical casing disposed within said tube with its widest portion sealed downstream in the tube and constituting a dischareg end for products of combustion, which discharge end is of an angle to closely encompass the outer end of the hollow conical spray pattern, and

said conical casing having an apex with an opening of a size to accommodate the nozzle in a position to discharge its conical spray within the conical casing and longitudinally thereof, the included angle of the conical casing being less than the external angle of the spray pattern and providing a clearance space between the conical casing and spray pattern of progressively diminishing size outwardly which extends substantially throughout the length of the conical casing, an outward portion of said conical casing having a grouping comprising a multiplicity of small air holes, the first holes of said grouping being a substantial distance outwardly from the nozzle with the holes of said grouping covering substantially the remainder of the casing outwardly and substantially to the discharge end, said air holes being adapted to project jets of combustion air inwardly and at substantially right angles to the outer surface of the spray patterns whereby the finely divided fuel spray pattern is penetrated inwardly by a multiplicity of jets of air to effect rapid and thorough mixing of fuel and air in uniform proportions to cause hydroxylation and combustion to occur with short flames at a uniformly low temperature and without formation of carbon.

7. A gas turbine combustor as claimed in claim 6 in which the air holes are arranged generally in closelyspaced formation.

8. A gas turbine combustor as claimed in claim 6 in which the first air holes of said grouping are removed from the nozzle a distance D which is between 15% and 50% of the distance D, which latter distance is a length along the slant height of the conical casing measured from its apex to the outer end of the grouping of air holes.

9. A gas turbine combustor as claimed in claim 6 in which the first air holes of said grouping are removed from the nozzle a distance D which is approximately one-third of D, which latter distance is a length along the slant height of the conical casing measured from its apex to the outer end of the grouping of air holes.

10. A gas turbine combustor as claimed in claim 6 in which the diameter of an air hole is between 1% and 4% of the distance D, which latter distance is a length along the slant height of the conical casing measured from its apex to the outer end of the grouping of air holes.

11. A gas turbine combustor as claimed in claim 6 in which the maximum radial width X of the clearance space X between the conical casing and spray pattern is between 4% and 6% of D, which latter distance is a. length along the slant height of the conical casing measured from its apex to the outer end of the grouping of air holes.

12. A gas turbine combustor as claimed in claim 6 in which the maximum radial width W of the spray pattern is between 10% and 50% of D, which latter distance is a length along the slant height of the conical casing measured from its apex to the outer end of the grouping of air holes.

13. A gas turbine combustor as claimed in claim 6 in which the sum of the areas of the multiplicity of small airholes is 30%60% of the area of that conical casing portion which has such holes.

14. A combustor comprising a hollow conical casing, a fuel spray nozzle of the hollow cone type mounted within the apeX end of said hollow conical casing in such manner as to provide for projecting a diverging hollow conical spray of liquid fuel generally parallel with but spaced inwardly from the inner surface of said hollow conical casing, said casing being foraminated in a region spaced outwardly from the apex and continuing outwardly a substantial distance to present a band of closely spaced perforations constituting small air inlet ports and said casing being imperforate in a region between its apex and said foraminated region to provide a shield, and the interior of the casing being free of obstructions to inward and reverse flow within the casing, whereby combustion air may be projected inwardly through said ports as a 11 multiplicity of individual small jets penetrating transversely into the hollow conical spray of fuel to eifect rapid and thorough mixing of air and fuel at uniform ratios for hydroxylation to highly combustible gases and then for burning at uniform relatively low temperature 5 with short flames without forming elemental carbon.

References Cited UNITED STATES PATENTS 3,075,352 1/1963 Shutts 60-3965 3,229,464 1/1966 Mock 60---39.65 3,360,929 1/ 1968 Drewry 60-39.65

CARLTON R. CROYLE, Primary Examiner DOUGLAS HART, Assistant Examiner US. Cl. X.R. 

